1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for producing the same, and more particularly to a liquid crystal display device having a wide viewing angle characteristic and a method for producing the same.
2. Description of the Background Art
Liquid crystal display devices of various display modes have been widely used in the art, including a TN mode and an STN mode in which an image is displayed by untying a twist alignment of liquid crystal molecules by applying a voltage across a liquid crystal layer, and an ECB mode in which an image is displayed by utilizing changes in birefringence due to changes in orientation of the liquid crystal layer that are caused by a voltage application. However, liquid crystal display devices of these display modes have a poor viewing angle characteristic.
As liquid crystal display devices become more widespread, there are more stringent characteristics requirements. For example, there has been a demand for liquid crystal display devices having wide viewing angle characteristics suitable for use in personal digital assistants, personal computers, word processors, amusement equipment, educational equipment, television sets, etc., that are viewed by a number of viewers.
Known methods for improving the viewing angle characteristic of a liquid crystal display device include a so-called “pixel division method” (also called “multi-domain method”).
For example, Kato, et. al., have proposed a TN-alignment 4-division method using a nematic (Np) liquid crystal material having a positive dielectric anisotropy and a horizontal alignment film in IDW'97, p.163–p.166, “Four-Domain TN-LCD Using New Division Pattern and Special Arrangement”. It is stated that with the 4-division method of this article, there is no disclination line occurring between domains, which has been a problem with TN-alignment pixel division methods. However, in a normally white mode (NW mode) TN type liquid crystal display device, typically, light leakage is likely to occur in a black display, and it is difficult to realize a display with a high contrast ratio. This is due to liquid crystal molecules in the vicinity of an alignment film (sometimes called an “anchoring layer”) maintaining a horizontal alignment even in the presence of an applied voltage. Therefore, with the 4-division TN type liquid crystal display device disclosed in the above article, as with other TN type liquid crystal display devices, it is difficult to realize a high-quality display that is currently demanded.
Japanese Laid-Open Patent Publication No. 10-301113 describes improving the viewing angle characteristic and the response characteristic of a liquid crystal display device of a vertical alignment type by forming a minute domain in a boundary region between two domains in which liquid crystal molecules are inclined in respective directions differing from each other by 180° so that the liquid crystal molecules in the minute domain are inclined in a direction that is perpendicular to both of the respective directions in which the liquid crystal molecules are inclined in the two domains. Since the liquid crystal display device is of a vertical alignment type, the quality of a black display is not lowered as in a TN type liquid crystal display device.
However, the present inventors have found that with the vertical alignment type liquid crystal display device disclosed in this publication, a disclination line occurs between domains as a voltage is turned ON/OFF. As a result, a display non-uniformity is observed in all azimuth angle directions particularly when the display surface is observed from an inclined direction. If the disclination line occurs to a considerable degree, the display quality is dependent on the viewing angle.